I cannot recall where I once read a list of popularity of instruments to learn that placed Double Bass almost at the bottom - I think the bottom was Tuba. My impression is that the bass, in all its forms of genre, is a far more active and attractive instrument in American musical life than here in Australia. Prior to Covid a teacher of violin, flute , piano or singing in Sydney could easily fill their books seven days a week. Lots of schools, especially the wealthier private ones, had very healthy music departments and ensembles as extra-curricular activities (like sports, etc). We also have youth orchestras, the best organisation being Sydney Youth Orchestra that advances young players in stepped ensembles towards selection for the Australian Youth Orchestra as a pathway towards being professionals. So, we do have quite a lot of school-age bass students however this still only translates to a few school-leavers interested in auditioning for the degree course at our Conservatorium of Music and a career in music. Most of the bright advanced ones look first to medicine, economics, commerce, law (money, jobs, status.......). For all the time, effort and money spent by parents on bass lessons very few ex-students go on to play in amateur orchestras unless it is later in their careers. I play as a guest in the NSW Doctors Orchestra that calls itself Musicus Medicus.
Why all the preamble above? We just don't have a big enough pool of capable older amateur bass players interested in orchestral music ! In Sydney I can think of twenty-one organisations who would love to have more strings, especially violas and bass players. The young aspirants at the Conservatorium are not interested in mere petrol money. At the end of my career as a professional who was until recently paid to come in and play with some of these orchestras I decided to join one of the best that rehearses and performs ten minutes away. Two basses trying to balance an orchestra of 45 is to suddenly reduce to one - me !! My stand partner is bailing out to finish studying for an advanced Commercial Pilot's Licence - 5 subjects to go.
Cheers, Andy, your thread is timely as it reminds me to get off my butt and find a new member or two for my orchestra.